There is known in the art a method of treating pyrite concentrate, which comprises heating (roasting) this material in an atmosphere of inert gas without air access, and then subjecting it to flash roasting at a temperature of 1800.degree. to 2000.degree. C. Here, the pyrite concentrate, containing 46 percent by weight of iron and 52.8 percent by weight of sulphur, is subjected to thermal decomposition with the resultant formation of matte and separation of elemental sulphur. The matte is granulated to be thereafter roasted in a furnace in a fluidized bed, this being accompanied by the liberation of sulphurous gases intended for further use in the production of sulphuric acid. The resultant iron concentrate may contain up to 67 percent by weight of iron.
The above method, however, is suitable for the treatment of sulphur-rich pyrite concentrate, with no recovery of nonferrous, noble and rare metals.
There is known a method of treating pyrite concentrates less rich in sulphur and iron, containing 38.5 percent by weight of iron, 39.1 percent by weight of sulphur and 20 percent by weight of gangue. This method comprises oxidizing roasting of the initial material, which is carried out in a furnace in a fluidized bed at a temperature of 965.degree. C. The resultant roast is then subjected to reducing magnetizing roasting at a temperature of 550.degree. to 650.degree. C., to be followed by magnetic separation thereof. The oxidized roast undergoes magnetic separation with a field intensity of 100 to 600 oersted. The resultant magnetic product undergoes pelletizing and firing, whereafter it contains 66 percent by weight of iron, thus being rendered suitable for blast-furnace smelting.
The method described above is also unsuitable for the recovery of nonferrous, rare and noble metals. To accomplish the recovery of these metals and to expand the scope of application of the pyrite material being treated, it is necessary that the two above-mentioned methods should include the operation of chloride sublimation to be effected in a fluidized bed at a temperature of 1250.degree. C. This, however, will render the technological process much more complicated and the equipment cost greatly increased.
To carry out the recovery of nonferrous and noble metals from pyrite concentrates, the initial material is to be subjected to oxidizing roasting effected in a furnace in a fluidized bed at a temperature of 900.degree. C. The off-gases are used for the production of sulphuric acid, and the oxidized roast is granulated in 40%-solution of calcium chloride, whereupon it is subjected to secondary roasting carried out at a temperature of 1250.degree. C. in cylindrical rotary kilns. The resultant granulated iron-containing product is used in blast furnaces. The gases evolved in the process of secondary roasting contain chlorides of nonferrous and noble metals.
The above-described method, includes two-stage roasting of high-grade concentrates and, on being effected at high temperatures, substantially increases the operating cost.
Another known method used for the recovery of nonferrous and noble metals from polymetallic material comprises subjecting this material to reducing roasting, which is effected in a furnace in a fluidized bed at a temperature of 704.degree. to 816.degree. C. and proceeds until pyrrhotine is obtained. The pyrrhotine is then subjected to aqueous lixivitation in an autoclave, with oxygen under pressure being fed therein. The nonferrous metals are passed on to a solution to be further separated therefrom by means of hydrogen sulphide.
However, the roasting procedure combined with the autoclave lixiviation and subsequent hydrometallurgical recovery of nonferrous metals renders the above method cumbersome and complicated.
Various techniques employed today in the treatment of rebellious polymetallic ores, notwithstanding numerous modifications and improvements, fail to satisfy the growing demands of nonferrous metallurgy in high-grade selective concentrates. Thus, the increase of total volume of pyrite bearing polymetallic concentrates, intermediary products and tails makes it absolutely necessary and essential to develop effective and comprehensive methods of treating these types of materials so as to obtain therefrom valuable products, such as elemental sulphur, iron-ore pellets and concentrates of nonferrous metals.